1. Field of the Invention
This invention relates to an explosion-proof type rotating electrical machine capable of operating in an atmosphere of flammable gas.
2. Description of the Related Art
Conventionally, a synchronous machine and a DC machine each of the type having a field coil produce sparks between conductive contact members such as slip rings, a commutator etc and slip rings, accordingly when those rotating electrical machines are operated in a flammable gas atmosphere, such sparks tend to fire up the flammable gas generating flames.
For this reason, the explosion-proof type rotating electrical machine capable of preventing the flammable gas from being ignited has conventionally been employed for ships. For such explosion-proof type rotating electrical machines, well known examples are an enclosed type where an entire rotating electrical machine is sealed as disclosed in U.S. Pat. No. 4,680,495 and a wire net type where entire inlet and outlet ports of air of the rotating electrical machine are covered with a flame stifling wire net to prevent the flames within the rotating electrical machine from leaking to the outside of such rotating electrical machine as disclosed in Japanese Utility Model Registration Patent Application Laid Open 51054 in 1975.
An example of a wire net type rotating electrical machine is shown in FIG. 14. The flame stifling wire nets 104 and 105 are each arranged on an air suction inlet 101 holed in a rear housing 100 and an air discharge outlet 103 holed in a front housing 102. Numeral 106 depicts a cooling fan.
However, when the enclosed type is used, an output thereof is largely reduced due to lack of cooling capability, and volume and weight of the rotating electrical machine are considerably increased in order to obtain a required output.
Even in the case of wire net type, the flame stifling wire net, which covers the air inlet and outlet ports, inevitably increases ventilation resistance, resulting inevitably in an output reduction due to poor cooling capability, and increases of volume and weight.
Also, sealing a small space (hereinafter referred to as a brush compartment) embracing the conductive contact members and the brushes can be considered, but in such a structure, brush powders produced by wear of the brushes build up in the brush compartment, as a result, there is a possibility to cause a short-circuit accident between the slip rings or the like.